Embodiments of the present invention relate to an imaging device for forming an image on an image sensor.
An imaging device 20 comprises a lens module 24 which directs an image onto an image sensor 28, as for example shown in FIG. 1. The lens module 24 comprises a lens 30 mounted in a lens barrel 32, the exterior surface of which comprises a screw thread 33. The image sensor 28 can be, for example, a CCD or CMOS array having an image receiving surface 36 comprising imaging pixels 38 which convert an incident image of light, infra-red or other radiation, into an electric signal. Typically, the image sensor 28 is enclosed in a package 40 which can include one or more cover plates 41, which are transparent to light and protect the image sensor 28. A holder 42 comprising an interior screw thread 43 joins and aligns the lens 30 in the lens module 24 to the image sensor 28 in the package 40. The imaging device 20 is used in, for example, electronic devices such as mobile phones, personal digital assistants, remote sensors, signal transmitting cameras, medical devices, and applications such as lenses for car security systems.
As such imaging devices 20 are developed to have smaller sizes, it becomes increasingly difficult to properly position and align the ever smaller lenses 30 to the plane of the image receiving surface 36 of the image sensor 28. For example, it can be difficult to align the axis of a lens 30 to be parallel to the central axis of a lens barrel 32 during assembly of the lens module 24. Even a slight degree of misalignment will cause the image generated by a lens 30 to become unfocused. Also, the lens 30 has to be at a particular height above the image sensor 28 to provide a properly focused image on the sensor 28. During focus testing, the spacing between the lens 30 and image sensor 28 is changed by adjusting the height of the lens barrel 32 having a screw thread 33 inside the lens holder 42. However, the screw threads 33 and 43 have to be very accurate to provide sufficiently small incremental height adjustments, which may be as small as 1 micron, without un-centering the lens 30 or causing the lens 30 to tilt. The focus testing and height adjustment step increases assembly costs and can result in assembly defects and lower device yields.
For various reasons that include these and other deficiencies, and despite the development of various imaging devices, further improvements in imaging device design and assembly are continuously being sought.